Process of producing manganese



United States Patent 3,054,670 PROCESS OF PRODUCING MANGANESE Andre Gretfe, Annecy, Maurice Asselin, Moutiers, and

This invention relates to a process of producing manganese by distilling manganese from a molten bath of high-carbon ferromanganese.

It is known to produce manganese by vacuum distillation of an alloy containing it. In particular, ferromanganese may be used as starting material. The distillation of ferromanganese containing about 6 to 7% carbon, produced in the blast furnace or electric furnace, is of the most economic interest.

However, the use of high-carbon ferromanganese as starting material gives rise to difl'iculties. It has been proposed to distill manganese from such starting material under a pressure comprised between and 10- mm. of mercury and at a temperature comprised between 1200 and 1300 C. But this process requires that, up to the end of the distillation, the molten bath be not saturated in carbon. If one exceeds the state of saturation, a layer of graphite is formed on the surface of the bath which hinders further distillation. Furthermore, it has been proved experimentally that a rapid elevation of the temperature above the fusing point produces a relatively slow evaporation speed.

Various methods have been proposed to obtain at one and the same time a high evaporation speed and a great extraction of manganese. According to French Patent 1,160,614 particularly, it is necessary to use as starting material arefined ferromanganese containing at most 1% of carbon, excluding a more highly carburated ferromanganese, i.e. 6 to 7% of carbon. According to this patent, the use of such more highly carburated ferromanganese would effectively require limiting the manganese extraction to a value where the process would not be economical.

It has also been suggested to carry out the vacuum distillation of carburated ferromanganese by charging the granular product, the individuality of which is preserved, without apparent fusion during the treatment. The manganese evaporation speed is acceptable, if one proceeds by steps at increasing temperatures. The temperature used in the first step is then lower than the fusing temperature of the alloy, which causes at the periphery of each grain the formation of a graphitic but porous layer, through which the distillation is produced during the further steps at temperatures above the fusing temperature. Each liquid grain is thus enclosed in a graphite envelope and isolated from the neighboring grains. But a grinding is necessary and the treatments are long, the distillation itself taking 24 hours.

Recently it has been proposed to use ferromanganese finely ground and mixed with carbon grains of the same granulometry in sufiicient quantity in order to establish a kind of screen between the alloy grains and to avoid their coalescence. The mixture is then heated directly to a temperature above the fusion point of the ferromanganese. But this process requires a preliminary grinding with all the disadvantages that such treatment entails. Besides, a magma containing particles of non-recoverable manganese may be formed.

The obtaining of metal manganese by vacuum distillation of manganese from a molten bath of ferromanganese is therefore actually impossible, owing to the formation of a non-permeable carbon layer on the bath surface.

3,054,670 Patented Sept. 18, 1962 ice The present invention solves this problem. It consists in fixing the carbon of the melted ferromanganese in the bath, by adding to the bath, wholly from the beginning of the fusion or progressively, such a quantity of iron, that account being taken of the iron coming from the ferromanganese, the carbon is constantly dissolved entirely in the bath as it is liberated from its combination with the ferromanganese during the distillation of the manganese, and that finally a pig iron is obtained.

The quantity of iron to be added is determined in each particular case, taking into account the initial contents of iron and carbon in the ferromanganese, the temperature of distillation and the known Fe-C diagram in order that, up to the end of the distillation, the carbon remains in the bath and does not form a separate phase which would rise to the surface. For example, for a distillation temperature of 1200 C., for each kg. of ferromanganese containing Mn, 12% Fe and 7% carbon, it is necessary to add at least 1.36 kg. of Fe. The addition of iron may be advantageously made in the form of scrap iron and account should be taken of the carbon content of the scrap iron in calculating the quantity of scrap iron to be added.

The distillation temperature is advantageously comprised between 1200 and 1300 C. The distillation pressures may vary between 1 mm. and 10 mm. of mercury.

The distillation may be conducted until a very complete extraction of manganese is obtained, i.e. until 95% or even more is extracted, which, account being taken of the losses in the vacuum pump, allows the recovery in form of manganese of more than of manganese metal.

The obtained metal is of excellent quality; its manganese content is generally above 90%. The Fe and C contents may be as low as 0.1%. The product remaining in the distillation furnace is a saleable pig iron, the Mn content of which is in the range of currently-sold pig irons.

The process according to the invention presents the great economic advantage of making use only of relatively cheap high-carbon ferromanganese and scrap iron, the scrap iron being transformed during the operation into pig iron, the value of which is at least as great as that of scrap iron. Besides, the distillation is rapid and may be conducted until a recovery of at least 90% of the manganese is obtained.

The following example further illustrates the process.

Example Gas was carefully removed from a furnace by the application of a vacuum, and then the furnace was charged with 200 kg. of high-carbon ferromanganese having the composition 80% Mn, 12% Fe and 7% C, together with 400 kg. of scrap iron having the composition 99% Fe, and 0.060% C.

The charge was melted under a low argon pressure and then the pressure was progressively lowered and the vacuum distillation of manganese was maintained under apressure of about 0.5 mm. of mercury and at a temperature of about 1300 C. At the end of one hour and 15 minutes, 146 kg. of manganese metal having a carbon content of 0.10% and an iron content of 0.15% had been extracted. This amount of manganese, based on the manganese initially contained in the high-carbon ferromanganese, corresponded to a yield of 91%. On the other hand, there was obtained a residuary pig iron in the amount of 450 kg, this pig iron having a manganese content of about 1% and a carbon content of about 3.12%

The invention is not limited to the preferred embodiment, but may be otherwise embodied or practiced within the scope of the following claim.

We claim:

A process of obtaining manganese, which comprises forming a molten bath of high-carbon ferromanganese and added iron, and distilling manganese from the molten bath at a temperature between 1200 and 1300 C. and at a pressure between 1 mm. and 10* mm. of mercury, the quantity of added iron being such that, taking into account the iron coming from the ferromanganese, the carbon isconstantly dissolved entirely in the bath as it is liberated from its combination with the ferromanganese during the distillation of the manganese and that a pig iron is obtained.

References Cited in the file of this patent FOREIGN PATENTS 840,803 Great Britain July '13, 1960 5 OTHER REFERENCES stracts, vol. 24, 195657 (New Series), London, 1957, 

